Isotope best dating very old rocks
“Nobody thought that was the case five years ago.” The team produced a new, average figure for the uranium ratios.It shifts the ages of Earth’s oldest rocks slightly, by just under a million years, Hiess says.Two of the solar system’s best natural timekeepers have been caught misbehaving, suggesting that the accepted ages for the oldest known rock samples are off by a million years or more.According to two new studies, a radioactive version of the element samarium decays much more quickly than previously thought, and different versions of uranium don’t always appear in the same relative quantities in earthly rocks.But Paul and colleagues suspected that that number wasn’t quite right.
“These are two big steps in improving the way we do geochronology, both in the solar system and terrestrial rocks,” Brennecka says.
But high-precision measurements of early materials found in meteorites or rocks formed in oceans showed differences.
Hiess and colleagues made the most wide-ranging study of uranium isotope ratios yet, using 45 samples of zircon from all over the world (pictured, above right).
The oldest rocks will have the biggest corrections: sediments that are 4.4 billion years old are now younger by 700,000 years.
“To put it into a human perspective, if the Earth was only 18 years old, we have taken 1 day off the life of its oldest materials,” Hiess says.
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